SANFORD — A 39-year-old Sanford man remained in critical condition Wednesday after being burned over more than 90 percent of his body on Tuesday afternoon.

Thomas Basinger, of 572 Lebanon Road, was transported by ambulance to Massachusetts General Hospital in Boston after he was seriously burned while tending to his outdoor wood furnace.

Fire investigators believe that a flammable liquid likely exploded as Basinger was attempting to stoke the fire in the wood furnace, located in his backyard.

Basinger’s wife, Karie, heard her husband’s cries for help and used a garden hose to extinguish the fire and a passing motorist pulled in the driveway to help, according to Sanford Fire Chief Jeffrey Rowe.

The Sanford Regional Communications Center received the emergency call at 4:18 p.m. Rowe said fire and rescue workers believed at first that it was a structure fire resulting from an explosion in a traditional indoor furnace. They responded with several fire engines and the ladder truck, as well as a rescue unit and learned the details as they sped to the scene.

Basinger was transported to Goodall Hospital and was awaiting transport via LifeFlight helicopter to Massachusetts General Hospital. The LifeFlight helicopter was busy, and a second contact — the Dartmouth-Hitchcock Hospital helicopter service — was grounded due to a passing storm. So Basinger was ultimately transported to Boston in a Sanford ambulance which left Sanford at about 5:45 p.m.

Investigators are attempting to determine the type of flammable liquid Basinger was using, according to the State Fire Marshal’s Office.Friends and family members have established a fund to help the Basingers with medical bills and other expenses. Donations may be made at any TD Bank; please reference “Verna — Tom Basinger.”